1. Field of the Invention
The present invention relates to a multi-level wiring structure and, more particularly, to a multi-level wiring structure using an organic insulating film as an interlayer insulating film.
2. Description of the Prior Art
It has been known that a multi-level wiring structure is formed by using an inorganic insulating film as the interlayer insulating film. As an example of the structure, a three level wiring structure may be considered. In the structure, a first wiring layer is formed on a surface of an inorganic insulating base, a first inorganic insulating film, for example a silicon oxide film, is formed to cover the surface of the first wiring layer and the inorganic insulating base, consecutively. At the surface of the inorganic insulating film, a second wiring layer is formed. A second inorganic insulating film, for example a silicon oxide film, is formed to cover the surface of the second wiring layer and the first inorganic insulating film, consecutively. At the surface of the second insulating film, a third wiring layer is formed. A via hole is formed at a predetermined part of the first inorganic insulating film, and the first wiring layer and the second wiring layer are connected electrically by filling metal in the hole. In the case of the multi-level wiring structure using the inorganic insulating film as the interlayer insulating film, the hardness of the silicon oxide film is more than 1000. Therefore, one can carry out wire bonding to any bonding pad even if the pad is made of each part of the first, the second or the third wiring layer.
Now a three level wiring structure made by using an organic insulating material such as polyimide resin or epoxy resin instead of the first and the second inorganic insulating film for interlayer insulating film will be considered. In this prototype, as the first wiring layer is formed on the surface of the inorganic insulating layer, wire bonding is carried out well even if the bonding pad is made of one part of the first wiring layer. However, the wire bonding to a bonding pad made of one part of the second and the third wiring layers is not carried out stably. The reason is that as the hardness of the organic insulating film is much smaller than that of inorganic insulating film, the force of pressure welding is absorbed even if the bonding wire is pushed to the pad.